248 bulletin: museum of comparative zoology. 



might be two reasons for questioning my generic reference : the first is, I have 

 not stated whether the synapticulse are true or false. As no thin section was 

 made, this point of structure could not be determined. But I do not believe 

 in the systematic value of dividing synapticulse ^ into true and false. Whether 

 the synapticulse are true or false depends largely upon spacial relations, as do 

 many other microscopic features of the coral skeleton. If the septa are 

 crowded the synapticulse are apt to be false, while if they are more remote 

 from each other the synapticulse are apt to be true. Figure 71, in Miss 

 Ogilvie's " Microscopic and Systematic Study of Madreporarian Types of 

 Corals," 2 is a good illustration of this. This figure represents two adjoining 

 septa of Siderastrcea. Near the peripheral ends of the septa the synapticulse 

 are true, i.e. there are new calcification centers introduced to effect the junc- 

 tion of the opposing septal granulations ; whereas, near the inner ends of the 

 septa, where the opposing septal surfaces are close together, no additional 

 centers of calcification are needed to make the junction of the granulations, so 

 they fuse directly and form a pseudo-synapticula. 



Probably another note should be added on the septal structure. The trabecu- 

 lar composition has already been noted. In the lower part of the calices the 

 trabecular fusion seems perfect, but near the septal margins the fusion appar- 

 ently may quite often be incomplete. Here pits are very distinct on the flat 

 surfaces of the septa, should the septa be not completely perforated. This 

 might be a second reason for the removal of the species from Mesomorpha, 



It was not determined whether dissepiments are present or not. 



Species of Mesomorpha occur in the Gosau Cretaceous and in the Eocene of 

 the Arabian Desert. Pratz is of the opinion that Thamnastrcea ferojuliensisj 

 d'Achiardi, from the Italian Eocene, and Thamnastrcea halli^ Duncan, from 

 the lower Eocene of India, also belong to this genus. 



DENDRACIS, Edwards and Haimb. 

 Dendracis cantabrigiensis, sp. nov. 



Plate XLI. Figs. 4-6. 



The corallum is composed of small slender branches from 3.5 to 8.5 mm. in 

 diameter. The branch 3.5 mm. in diameter is 26 mm. long. There is no 

 means of knowing to what length the thicker branches will attain. The 

 calices are distributed in rather regular spirals ; the usual diameter is 1 mm , 

 and the distance apart also usually 1 mm. On very small branches some 

 calices may have a diameter very slightly less than a millimeter, and may be a 



1 Consult G. von Koch : " Das Skclett der Steinkorallen," Festschrift f iir Carl 

 Gegeiibauer, 181)6, p. 2G0. 



2 Phil. Trans. Key. Society, 189G, Vol. 187, p. 244. 



